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//
// Copyright 2016 Charles W. Rapp
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//

package net.sf.eBus.client;

/**
 * An eBus client implementing either {@code ESubscriber},
 * {@code EPublisher}, or {@code ERequestor} is not required
 * to override the matching feed status method (
 * {@link ESubscriber#feedStatus(EFeedState, IESubscribeFeed)},
 * {@link EPublisher#publishStatus(EFeedState, IEPublishFeed)}, or
 * {@link ERequestor#feedStatus(EFeedState, IERequestFeed)}).
 * Instead, a lambda expression implementing this interface may
 * be used as the callback. This allows for tighter coupling
 * between the status callback and the code for handling the
 * callback.
 * 
 * Note: This must be done after opening a feed and before
 * advertising or subscribing.
 * 
 *
 * @author Charles W. Rapp
 *
 * @param  must be either {@link ERequestFeed},
 * {@link ESubscribeFeed}, or {@link EPublishFeed}.
 *
 * @see EPublishFeed.Builder#statusCallback(FeedStatusCallback)
 * @see ESubscribeFeed.Builder#statusCallback(FeedStatusCallback)
 * @see ERequestFeed.Builder#statusCallback(FeedStatusCallback)
 */

@FunctionalInterface
public interface FeedStatusCallback
{
//---------------------------------------------------------------
// Member methods.
//

    /**
     * eBus calls this method to inform the eBus client that the
     * feed is either
     * {@link EFeedState#UP up} or {@link EFeedState#DOWN down}.
     * @param feedState the subscription's new feed state.
     * @param feed the status applies to this feed.
     */
    void call(EFeedState feedState, T feed);
} // end of interface FeedStatusCallback